U.S. patent application number 15/254532 was filed with the patent office on 2017-05-11 for apparatus employing shear forces to transmit energy having flow altering structures configured to increase heat rejection from a working fluid and related method.
The applicant listed for this patent is BorgWarner Inc.. Invention is credited to Samuel E. Settineri, Jonathan B. Stagg.
Application Number | 20170130783 15/254532 |
Document ID | / |
Family ID | 57120826 |
Filed Date | 2017-05-11 |
United States Patent
Application |
20170130783 |
Kind Code |
A1 |
Stagg; Jonathan B. ; et
al. |
May 11, 2017 |
APPARATUS EMPLOYING SHEAR FORCES TO TRANSMIT ENERGY HAVING FLOW
ALTERING STRUCTURES CONFIGURED TO INCREASE HEAT REJECTION FROM A
WORKING FLUID AND RELATED METHOD
Abstract
A device that employs shear forces to transmit energy includes
an outer housing assembly, a disk, and a reservoir with a working
fluid. The disk is received in and rotatable relative to the outer
housing assembly. A working cavity is formed between a rotor
portion of the disk and the outer housing assembly into which the
working fluid is received to create shear forces. A plurality of
flow altering structures are disposed on the outer housing assembly
and are configured to reduce a thickness of a boundary layer of the
working fluid in the working cavity in areas that are local to the
flow altering structures.
Inventors: |
Stagg; Jonathan B.;
(Bellevue, MI) ; Settineri; Samuel E.; (Marshall,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BorgWarner Inc. |
Auburn Hills |
MI |
US |
|
|
Family ID: |
57120826 |
Appl. No.: |
15/254532 |
Filed: |
September 1, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15091606 |
Apr 6, 2016 |
9470278 |
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15254532 |
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62253652 |
Nov 10, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F16D 35/02 20130101;
F16D 35/021 20130101; F16D 2300/021 20130101; F16D 2250/003
20130101; F16D 2300/10 20130101; F16D 2250/0007 20130101; F16D
2250/0023 20130101 |
International
Class: |
F16D 33/20 20060101
F16D033/20 |
Claims
1. An apparatus comprising: an outer housing assembly having a
working cavity that is bounded by a first annular wall, a second
annular wall and a circumferentially extending wall that is
disposed between and connects the first and second annular walls,
the first annular wall having a plurality of first concentric fluid
grooves; a disk that is rotatably received in the outer housing
assembly, the disk having a rotor portion that is received in the
working cavity, the rotor portion having a first side, a second
side and an outer circumferential surface, the first side having a
plurality of first concentric ribs, each of the first concentric
ribs being received in an associated one of the plurality of first
concentric fluid grooves; and a reservoir that is adapted to hold a
working fluid therein, the reservoir being coupled in fluid
communication with the working cavity via a working fluid flow
path, the working fluid flow path having a first gap, which is
disposed axially between the first annular wall of the outer
housing assembly and the first side of the rotor portion, a second
gap, which is disposed axially between the second annular wall of
the outer housing assembly and the second side of the rotor
portion, and a third gap, which is disposed radially between the
circumferentially extending wall of the outer housing assembly and
the outer circumferential surface of the rotor portion; wherein at
least one of the first annular wall and the circumferentially
extending wall comprises a plurality of flow altering structures
that are configured to promote disturbances in a laminar flow of
the working fluid in an associated one or ones of the first and
third gaps in areas local to the flow altering structures when the
disk is rotated relative to the outer housing assembly and a
portion of the working fluid is in the working fluid flow path.
2. The apparatus of claim 1, wherein the flow altering structures
comprise cavities formed in the radially inner surface of the
circumferentially extending wall, each of the cavities extending
radially outwardly of the radially inner surface of the
circumferentially extending wall.
3. The apparatus of claim 2, wherein each cavity has a radially
outward wall that is at least partly concentric with the radially
inner surface of the circumferentially extending wall.
4. The apparatus of claim 2, wherein each of the cavities has a
pair of end segments that are disposed on opposite sides of a
radially outward wall, wherein at least a portion of one of the end
segments tapers between the radially outward wall and the radially
inner surface of the circumferentially extending wall.
5. The apparatus of claim 2, wherein each of the cavities has a
pair of end segments that are disposed on opposite sides on a
radially outward wall, each of the end segments connecting the
radially outward wall to the radially inner surface of the
circumferentially extending wall and at least one of the end
segments being defined at least partly by a radius.
6. The apparatus of claim 2, wherein each of the cavities has a
radial depth relative to the radially inner surface of the
circumferentially extending wall that is greater than or equal to
0.2 mm and less than or equal to 3.5 mm.
7. The apparatus of claim 6, wherein the radial depth of the
cavities is greater than or equal to 0.5 mm and less than or equal
to 2.8 mm.
8. The apparatus of claim 7, wherein the radial depth of the
cavities is greater than or equal to 0.8 mm and less than or equal
to 2.5 mm.
9. The apparatus of claim 2, wherein a theoretical cylinder is
defined by the radially inner surface of the circumferentially
extending wall, wherein the flow altering structures are disposed
on the radially inner surface of the circumferentially extending
wall within a contiguous zone, and wherein the flow altering
structures are sized and populated in the contiguous zone such that
the flow altering structures in the contiguous zone are disposed on
at least 50% of the surface area of the theoretical cylindrical
surface that lies within the contiguous zone.
10. The apparatus of claim 9, wherein the flow altering structures
are sized and populated in the contiguous zone such that the flow
altering structures in the contiguous zone are disposed on at least
75% of the surface area of the theoretical cylindrical surface that
lies within the contiguous zone.
11. The apparatus of claim 2, wherein each of the cavities has an
aspect ratio that is defined by the equation: AR=C/R where: C is a
maximum circumferential length of the cavity measured at the
radially inner surface of the circumferentially extending wall; and
R is a radial distance between a radially outer-most surface of the
cavity and a surface of the rotor portion taken along a line that
intersects a rotational axis of the disk; and wherein the aspect
ratio (AR) is greater than or equal to 0.2 and less than or equal
to 4.0.
12. The apparatus of claim 11, wherein the aspect ratio is greater
than or equal to 0.25 and less than or equal to 2.75.
13. The apparatus of claim 12, wherein the aspect ratio is greater
than or equal to 0.5 and less than or equal to 2.5.
14. The apparatus of claim 13, wherein the aspect ratio is greater
than or equal to 1.0 and less than or equal to 1.5.
15. The apparatus of claim 1, wherein the plurality of flow
altering structures number at least five (5) in quantity that are
disposed on the circumferentially extending wall.
16. The apparatus of claim 1, wherein at least a portion of the
plurality of flow altering structures are disposed on the
circumferentially extending wall such that they are not evenly
spaced about the circumference of the circumferentially extending
wall.
17. The apparatus of claim 16, wherein none of the flow altering
structures are disposed in a sector of the circumferentially
extending wall that spans at least 70 degrees.
18. The apparatus of claim 1, wherein the flow altering structures
comprise annular wall cavities formed in the first annular wall of
the outer housing assembly.
19. The apparatus of claim 18, wherein the first concentric fluid
grooves each define a flat annular root surface and wherein each of
the annular wall cavities intersects at least one of the flat
annular root surfaces.
20. The apparatus of claim 19, wherein each of the annular wall
cavities has a cavity sidewall and a cavity bottom wall that is
bounded by the cavity sidewall, and wherein at least a portion of
the cavity bottom wall is parallel to the at least one of the flat
annular root surfaces.
21. The apparatus of claim 19, wherein each of the annular wall
cavities has a pair of opposite circumferential ends and wherein at
least one of the circumferential ends is at least partly defined by
a radius at a location where the circumferential end intersects an
associated one of the flat annular root surfaces.
22. The apparatus of claim 19, wherein each of the annular wall
cavities has a depth relative to an associated one of the flat
annular root surfaces that is greater than or equal to 0.2 mm and
less than or equal to 3.5 mm.
23. The apparatus of claim 22, wherein the depth of the annular
wall cavities is greater than or equal to 0.5 mm and less than or
equal to 2.8 mm.
24. The apparatus of claim 23, wherein the depth of the annular
wall cavities is greater than or equal to 0.8 mm and less than or
equal to 2.5 mm.
25. The apparatus of claim 19, wherein each of the annular wall
cavities has a cavity sidewall and wherein at least a portion of
the cavity sidewall is perpendicular to an associated one of the
flat annular root surfaces at a location where the portion of the
cavity sidewall intersects the associated one of the flat annular
root surfaces.
26. The apparatus of claim 19, wherein the flow altering structures
on the first annular wall are disposed within one or more zones,
each of the zones being coincident with an associated one of the
flat annular root surfaces and having a planar annular shape or an
annular segment shape, and wherein the flow altering structures are
sized and populated in the one or more zones such that the flow
altering structures in the one or more zones are disposed over at
least 50% of the surface area of the one or more zones.
27. The apparatus of claim 26, wherein the flow altering structures
are sized and populated within the one or more zones such that the
flow altering structures in the one or more zones are disposed on
at least 75% of the surface area of the one or more zones.
28. The apparatus of claim 19, wherein each of the annular wall
cavities has an aspect ratio that is defined by the equation:
AR=C/R where: C is a maximum circumferential length of the annular
wall cavity measured at an associated one of the flat annular root
surfaces; and R is a maximum distance between a surface of the
annular wall cavity and a surface of an associated one of the first
concentric ribs taken parallel to an axis about which the disk
rotates relative to the outer housing assembly; and wherein the
aspect ratio (AR) is greater than or equal to 0.2 and less than or
equal to 4.0.
29. The apparatus of claim 28, wherein the aspect ratio is greater
than or equal to 0.25 and less than or equal to 2.75.
30. The apparatus of claim 29, wherein the aspect ratio is greater
than or equal to 0.5 and less than or equal to 2.5.
31. The apparatus of claim 30, wherein the aspect ratio is greater
than or equal to 1.0 and less than or equal to 1.5.
32. The apparatus of claim 1, wherein at least a portion of the
plurality of flow altering structures are disposed on the first
annular wall such that they are not evenly spaced about the
circumference of the first annular wall.
33. The apparatus of claim 32, wherein none of the flow altering
structures are disposed in a sector of the first annular wall that
spans at least 70 degrees.
34. The apparatus of claim 1, further comprising a valve in fluid
communication with the reservoir and the working cavity.
35. The apparatus of claim 34, wherein the valve is coupled to the
disk for rotation therewith.
36. The apparatus of claim 1, wherein the working fluid comprises
silicone.
37. The apparatus of claim 1, wherein the reservoir is at least
partly defined by the disk.
38. A method comprising: providing an apparatus having an outer
housing assembly, a disk and a reservoir, the outer housing
assembly having a working cavity, the disk being rotatable in the
outer housing assembly, the disk having a rotor portion that is
rotatably received in the working cavity, the working cavity being
in fluid communication with the reservoir; rotating the rotor
within the outer housing assembly to generate a flow of a working
fluid through the working cavity and to apply a shear force to the
working fluid flowing through working cavity; and inducing movement
of the working fluid at a plurality of locations on the outer
housing assembly in a direction that is transverse to a boundary
layer of the working fluid that is adjacent to the first annular
surface.
39. The method of claim 38, wherein the first surface is formed on
an annular wall of the outer housing assembly.
40. The method of claim 38, wherein the first surface is formed on
a circumferentially extending wall of the outer housing
assembly.
41. The method of claim 40, further comprising inducing
disturbances in a laminar flow of the working fluid in a second
area that is adjacent to a second surface of the working cavity as
the working fluid passes through the working cavity during
operation of the apparatus.
42. The method of claim 41, wherein the second surface is formed on
an annular wall of the outer housing assembly.
43. The method of claim 38, further comprising forming a plurality
of flow altering structures on the outer housing assembly.
44. The method of claim 43, wherein the flow altering structures
are unitarily formed with a portion of the outer housing assembly
that defines a plurality of concentric fluid grooves.
45. The method of claim 43, wherein the flow altering structures
are cavities.
46. The method of claim 45, further comprising casting at least a
portion of the outer housing assembly, wherein at least a portion
of the cavities are formed on the portion of the outer housing
assembly when the portion of the outer housing assembly is
cast.
47. The method of claim 45, further comprising removing material
from a portion of the outer housing assembly to form at least a
portion of the cavities.
48. The method of claim 47, wherein material is removed from the
portion of the outer housing assembly in an operation selected from
a group consisting of: milling, drilling, etching, broaching, and
electro-discharge machining.
49. The method of claim 38, further comprising forming a portion of
the outer housing assembly in an operation selected from a group
consisting of: stamping, embossing, forging, fine blanking and
knurling to form one or more flow altering structures.
50. The method of claim 38, wherein the locations on the outer
housing assembly are where the flow of the working fluid through
the working cavity has a Reynolds number that is less than 100.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 15/091,606 filed Apr. 6, 2016, which claims the benefit and
priority of U.S. Provisional Patent Application No. 62/253,652
filed Nov. 10, 2015. The disclosure of each of the above-referenced
patent applications is incorporated by reference as if fully set
forth in detail herein.
FIELD
[0002] The present disclosure relates to an apparatus employing
shear forces to transmit energy, such as a viscous fluid clutch, in
which the apparatus includes flow altering structures that are
configured to increase heat rejection from a working fluid.
BACKGROUND
[0003] This section provides background information related to the
present disclosure which is not necessarily prior art.
[0004] VISCTRONIC.RTM. fan drives that are commercially
manufactured by BorgWarner Inc. of Auburn Hills, Mich., are
examples of devices that employ shear forces on a working fluid to
transmit rotary power. In such devices, a relatively high viscosity
working fluid, such as a silicone fluid, is transmitted into a
working cavity between a disk and an outer housing assembly. The
disk is coupled to an input member for rotation therewith, while
the outer housing assembly can be coupled to a fan for common
rotation. The input member that drives the disk can be driven by a
belt of a front engine accessory drive that is driven by an
engine's crankshaft. The disk and the outer housing assembly
cooperate to form a flow path that is configured to generate shear
forces in the working fluid that in turn creates torque that drives
(i.e., rotates) the outer housing assembly. The generation of shear
forces in the working fluid, particularly when relatively high
levels of torque are desired, generates heat in the working
fluid.
[0005] To aid in rejecting heat from these devices, the outer
housing, which is commonly formed of aluminum, can be formed with a
plurality of cooling fins. The cooling fins effectively increase
the surface area of the exterior surface of the outer housing
assembly and increase the ability of these devices to reject heat
to the atmosphere via conduction, convection and radiation. The
cooling fins, however, do nothing to promote heat transfer from the
working fluid to the outer housing assembly.
[0006] The heat that is generated when the output housing assembly
slips relative to the input member is commonly called "slip heat".
The magnitude of "slip heat" generated at a given operational
condition is equivalent to the product of the fan torque at that
condition and the associated "slip speed" (i.e., the rotational
speed differential between input and output members). "Slip heat"
is therefore minimal at the extreme conditions of 0% slip and 100%
slip. In between these limits, in the region where output to input
speed ratio is around 50% to 60%, "slip heat" is generated at its
maximum rate. For this worst-case "slip heat" condition, only a
small portion of the available working fluid is present in the
working cavity; a majority of this smaller portion of fluid resides
in the region adjacent the OD of the rotor (disk). This creates a
particularly difficult problem to overcome; high "slip heat"
magnitude is entering into a relatively small volume of fluid that
has a relatively small wetted surface in contact with the walls of
the output housing. This problem has been present with all viscous
fan drives since the beginning of their usage in automotive engine
cooling circa 1950's-1960's.
[0007] We understand that a person of ordinary skill in the art
would have assumed that "slip heat" is an inherent problem and that
the above-described worst case "slip heat" condition simply must be
designed around, since the typical fluid shear gap between input
and output surfaces is generally very small (approximately 0.4 mm),
and it has not been conceivable that high thermal gradients could
exist in that tiny shearing region. Recent advances in fluid
material understanding have become possible through the utilization
of CFD (Computational Fluid Dynamics). In an effort to understand
how to optimize our invention to a given viscous fan clutch, we
investigated the thermal gradients that exist in the thin fluid
shear zone between the disk and the outer housing assembly (which
are typically rotating at different rotational speeds). Our
investigations of the thermal gradients that exist in the thin
fluid shear zone have revealed that completely laminar shear layers
are set up that do not effectively transport thermal energy from
layer to layer. Furthermore, we observed that the gradient
distribution tends to be very non-linear, which we believe to be
caused by the non-Newtonian nature of the silicone working fluid
that thins with both temperature and shear-rate. We observed this
non-linearity to cause the boundary layer adjacent the colder walls
of the output housing to be exceptionally thick and thermally
insulative.
[0008] U.S. Pat. No. 5,577,555 discloses a heat exchanger having a
stationary tube that is configured to transmit an aqueous solution
(e.g., "a lithium bromide aqueous solution including a surface
activating agent"). The tube defines a heat exchange wall having a
plurality of "dents" formed therein. The "dents" are described as
having a depth that is larger than a thickness of the tube wall and
between 0.6-2.0 mm. The size of the tube is not disclosed, but a
flow rate of the aqueous solution flowing through the tube is
"preferably 0.7-0.25 kg/(m.times.s)". While the '555 patent does
not describe the effect that the "dents" have on the aqueous
solution that flows through the tube, it appears to us that the
"dents" induce a transition from laminar flow to turbulent flow in
a portion of the flow of the aqueous solution that is near the wall
of the tube. If an aqueous solution of lithium bromide is assumed
to have a density of 1500 kg/m.sup.3, a dynamic viscosity of 0.006
Pasec, and a mass flowrate of 0.475 kg/sec, and the tube diameter
is assumed to be 25 mm, the average flow velocity would be 0.645
m/s. The corresponding Reynolds number is 4031.
[0009] In fluid mechanics, a dimensionless quantity known as a
Reynolds number is employed to predict flow patterns. The Reynolds
number is a ratio of inertial forces to viscous forces and can be
calculated by the following formula:
Re=(VL)/v
where Re is the Reynolds number, V is the fluid velocity, L is a
characteristic length, and v is the kinematic viscosity of the
fluid. In a pipe, laminar flow is associated with a Reynolds number
that is less than about 2000, turbulent flow is associated with a
Reynolds number that is greater than about 4000.
[0010] Accordingly, inducement of the transition from laminar flow
to turbulent flow in the tube disclosed in the '555 patent appears
to be possible due to a relatively high velocity of the aqueous
solution (which helps to provide a relatively large numerator in
the formula for calculating the Reynolds number) and a relatively
low kinematic viscosity of the aqueous solution (which provides a
relatively small denominator in the formula for calculating the
Reynolds number).
[0011] In contrast, the working fluid in the above described fan
drives is highly viscous (i.e., the parameter v in the denominator
of the formula for the Reynolds number is relatively large). As
such, the denominator in the formula for the Reynolds number is
relatively large so that the resulting Reynolds number is
relatively small so that inducement of turbulence is not possible.
For example, a fan drive operating at a 50% slip condition with a
slip speed of 1500 rpm in which the disk has a disk radius of 118
mm, a radial shear gap between the disk and the outer housing
assembly is 1.2 mm, and a kinematic viscosity of the working fluid
is 500 cSt at ambient temperature, the resulting Reynolds number is
44.5, which is significantly below a transition to turbulent flow
that begins at Reynolds numbers exceeding 2000.
[0012] In view of the above remarks, there remains a need in the
art for an apparatus that employs shear forces to transmit energy
in which the apparatus is better configured to reject heat from a
working fluid where turbulent flow mixing of the thermal boundary
layers is not a possibility.
SUMMARY
[0013] This section provides a general summary of the disclosure,
and is not a comprehensive disclosure of its full scope or all of
its features.
[0014] In one form, the present teachings provide an apparatus that
employs shear forces to transmit energy. The apparatus includes an
outer housing assembly, a disk and a reservoir. The outer housing
assembly has a working cavity that is bounded by a first annular
wall, a second annular wall and a circumferentially extending wall
that is disposed between and connects the first and second annular
walls. The first annular wall has a plurality of first concentric
fluid grooves. The disk is rotatably received in the outer housing
assembly and has a rotor portion that is received in the working
cavity. The rotor portion has a first side, a second side and an
outer circumferential surface. The first side has a plurality of
first concentric ribs and each of the first concentric ribs is
received in an associated one of the plurality of first concentric
fluid grooves. The reservoir has a working fluid therein and is
coupled in fluid communication with the working cavity. A working
fluid flow path extends between the reservoir and the working
cavity and includes a first gap, which is disposed axially between
the first annular wall of the outer housing assembly and a first
side of the rotor portion, a second gap, which is disposed axially
between the second annular wall of the outer housing assembly and a
second side of the rotor portion, and a third gap, which is
disposed radially between a radially inner surface of the
circumferentially extending wall of the outer housing assembly and
the outer circumferential surface of the rotor portion. At least
one of the first annular wall and the circumferentially extending
wall includes a plurality of flow altering structures that are
configured to reduce a thickness of a boundary layer of the working
fluid adjacent the at least one of the first annular wall and the
circumferentially extending wall at locations that are local to the
flow altering structures when the disk is rotated relative to the
outer housing assembly and a portion of the working fluid is in the
working fluid flow path. The reduction in the thickness of the
boundary layer of the working fluid is relative to a configuration
of the at least one of the first annular wall and the
circumferentially extending wall that does not comprise the
plurality of flow altering structures.
[0015] Configuration of the apparatus in this manner can induce
overall mixing of the shear layers to accomplish a more uniform
temperature gradient throughout the shear zone and/or can thin the
boundary layer on the relatively colder wall of the outer housing
assembly when the apparatus transmits rotary power through an
ultra-high viscosity, non-Newtonian shear-thinning and
temperature-thinning working fluid at a relatively high shear rate
in a relatively thin shear gap under flow conditions that are
associated with completely laminar flow (i.e., Reynolds numbers
that are significantly less than 500).
[0016] The flow altering structures can comprise cavities formed in
the radially inner surface of the circumferentially extending wall,
each of the cavities extending radially outwardly of the radially
inner surface of the circumferentially extending wall. Each cavity
can have a radially outward wall that is at least partly concentric
with the radially inner surface of the circumferentially extending
wall.
[0017] Each of the cavities can have a pair of end segments that
are disposed on opposite sides on a radially outward wall such that
at least a portion of one of the end segments tapers between the
radially outward wall and the radially inner surface of the
circumferentially extending wall.
[0018] Each of the cavities can have a pair of end segments that
are disposed on opposite sides on a radially outward wall such that
each of the end segments connects the radially outward wall to the
radially inner surface of the circumferentially extending wall and
at least one of the end segments is defined at least partly by a
radius.
[0019] Each of the cavities can have a radial depth relative to the
radially inner surface of the circumferentially extending wall that
is greater than or equal to 0.2 mm and less than or equal to 3.5
mm. The radial depth of the cavities can be greater than or equal
to 0.5 mm and less than or equal to 2.8 mm. Preferably, the radial
depth of the cavities is greater than or equal to 0.8 mm and less
than or equal to 2.5 mm.
[0020] A theoretical cylinder can be defined by the radially inner
surface of the circumferentially extending wall, wherein the flow
altering structures are disposed on the inner surface of the
circumferentially extending wall within a contiguous zone. The flow
altering structures can be sized and populated in the contiguous
zone such that the flow altering structures in the contiguous zone
are disposed on at least 50% of the surface area of the theoretical
cylindrical surface that lies within the contiguous zone.
Preferably, the flow altering structures are sized and populated in
the contiguous zone such that the flow altering structures in the
contiguous zone are disposed on at least 75% of the surface area of
the theoretical cylindrical surface that lies within the contiguous
zone.
[0021] Each of the cavities can have an aspect ratio that is
defined by the equation: AR=C/R, where: C is a maximum
circumferential length of the cavity measured at the radially inner
surface of the circumferentially extending wall; and R is a radial
distance between a radially outer-most surface of the cavity and a
surface of the rotor portion taken along a line that intersects a
rotational axis of the disk; and wherein the aspect ratio is
greater than or equal to 0.2 and less than or equal to 4.0.
Preferably, the aspect ratio is greater than or equal to 0.25 and
less than or equal to 2.75. More preferably, the aspect ratio is
greater than or equal to 0.5 and less than or equal to 2.5. Still
more preferably, the aspect ratio is greater than or equal to 1.0
and less than or equal to 1.5.
[0022] The plurality of flow altering structures can number at
least five (5) in quantity that are disposed on the
circumferentially extending wall.
[0023] At least a portion of the plurality of flow altering
structures can be disposed on the circumferentially extending wall
such that they are not evenly spaced about the circumference of the
circumferentially extending wall.
[0024] The apparatus can be configured such that none of the flow
altering structures are disposed in a sector of the
circumferentially extending wall that spans at least 70
degrees.
[0025] The first concentric fluid grooves can each define a flat
annular root surface and wherein the flow altering structures can
include annular wall cavities formed in the outer housing assembly
that intersect at least one of the flat annular root surfaces.
[0026] Each of the annular wall cavities can have a cavity sidewall
and a cavity bottom wall that is bounded by the cavity sidewall and
at least a portion of the cavity bottom wall can be parallel to the
at least one of the flat annular root surfaces.
[0027] Each of the annular wall cavities can have a pair of
opposite circumferential ends and at least one of the
circumferential ends can be at least partly defined by a radius at
a location where the circumferential end intersects an associated
one of the flat annular root surfaces.
[0028] Each of the annular wall cavities can have a depth relative
to an associated one of the flat annular root surfaces that is
greater than or equal to 0.2 mm and less than or equal to 3.5 mm.
Preferably, the depth of the annular wall cavities is greater than
or equal to 0.5 mm and less than or equal to 2.8 mm. More
preferably, the depth of the annular wall cavities is greater than
or equal to 0.8 mm and less than or equal to 2.5 mm.
[0029] Each of the annular wall cavities can have a cavity sidewall
and wherein at least a portion of the cavity sidewall is
perpendicular to an associated one of the flat annular root
surfaces at a location where the portion of the cavity sidewall
intersects the associated one of the flat annular root
surfaces.
[0030] The flow altering structures on the first annular wall can
be disposed within one or more zones in which each of the zones is
coincident with an associated one of the flat annular root surfaces
and has a planar annular shape or an annular segment shape. The
flow altering structures can be sized and populated in the one or
more zones such that the flow altering structures in the one or
more zones are disposed over at least 50% of the surface area of
the one or more zones. Preferably, the flow altering structures are
sized and populated within the one or more zones such that the flow
altering structures in the one or more zones are disposed on at
least 75% of the surface area of the one or more zones.
[0031] Each of the annular wall cavities can have an aspect ratio
that is defined by the equation: AR=C/R, where: C is a maximum
circumferential length of the annular wall cavity measured at an
associated one of the flat annular root surfaces; R is a maximum
distance between a surface of the annular wall cavity and a surface
of an associated one of the first concentric ribs taken parallel to
an axis about which the disk rotates relative to the outer housing
assembly; and the aspect ratio (AR) is greater than or equal to 0.2
and less than or equal to 4.0. Preferably, the aspect ratio is
greater than or equal to 0.25 and less than or equal to 2.75. More
preferably, the aspect ratio is greater than or equal to 0.5 and
less than or equal to 2.5. Still more preferably, the aspect ratio
is greater than or equal to 1.0 and less than or equal to 1.5.
[0032] At least a portion of the plurality of flow altering
structures can be disposed on the first annular wall such that they
are not evenly spaced about the circumference of the first annular
wall. For example, the apparatus can be configured such that none
of the flow altering structures are disposed in a sector of the
first annular wall that spans at least 70 degrees.
[0033] The apparatus can optionally include a valve in fluid
communication with the reservoir and the working cavity. The valve
can be coupled to the disk for rotation therewith.
[0034] The working fluid can comprise silicone.
[0035] The reservoir can be at least partly defined by the
disk.
[0036] In another form, the present teachings provide a method that
includes: providing an apparatus has an outer housing assembly, a
disk and a reservoir, the outer housing assembly has a working
cavity, the disk is rotatable in the outer housing assembly, the
disk has a rotor portion that is rotatably received in the working
cavity, the working cavity is in fluid communication with the
reservoir; rotating the rotor within the outer housing assembly to
generate a flow of a working fluid through the working cavity and
to apply a shear force to the working fluid flowing through working
cavity; and inducing movement of the working fluid at a plurality
of discrete locations on the outer housing assembly in a direction
that is transverse to a boundary layer of the working fluid that is
adjacent to the first annular surface.
[0037] The first surface can be formed on an annular wall of the
outer housing assembly or on a circumferentially extending wall of
the outer housing assembly.
[0038] If the first surface is a circumferentially extending wall
of the outer housing assembly, the method can further include
inducing disturbances in a laminar flow of the working fluid in a
second area that is adjacent a second surface of the working cavity
as the working fluid passes through the working cavity during
operation of the apparatus. The second surface can be formed on an
annular wall of the outer housing assembly.
[0039] The method can further include forming a plurality of flow
altering structures on the outer housing assembly. The flow
altering structures can be unitarily formed with a portion of the
outer housing assembly that defines a plurality of concentric fluid
grooves.
[0040] The flow altering structures can be formed as cavities.
[0041] The method can further include casting at least a portion of
the outer housing assembly such that at least a portion of the
cavities are formed on the portion of the outer housing assembly
when the portion of the outer housing assembly is cast.
[0042] The locations on the outer housing assembly can be where the
flow of the working fluid through the working cavity has a Reynolds
number that is less than 100.
[0043] The method can further include removing material from a
portion of the outer housing assembly to form at least a portion of
the cavities. Material can be removed from the portion of the outer
housing assembly in an operation selected from a group consisting
of: milling, drilling, etching, broaching, and electro-discharge
machining.
[0044] The method can further include forming a portion of the
outer housing assembly in an operation selected from a group
consisting of: stamping, embossing, forging, fine blanking and
knurling to form one or more flow altering structures.
[0045] In another form, the present teachings provide an apparatus
that includes an outer housing assembly, a disk that is rotatable
in the outer housing assembly and a reservoir. The outer housing
assembly has a working cavity that is bounded by a first annular
wall, a second annular wall and a circumferentially extending wall
that is disposed between and connects the first and second annular
walls. The first annular wall has a plurality of first concentric
fluid grooves. The second annular wall has a plurality of second
concentric fluid grooves. The disk has a rotor portion that is
received in the working cavity. The rotor portion has a first side,
a second side and an outer circumferential surface. The first side
has a plurality of first concentric ribs and the second side has a
plurality of second concentric ribs. Each of the first concentric
ribs is received in an associated one of the plurality of first
concentric fluid grooves. Each of the second concentric ribs is
received in an associated one of the plurality of second concentric
fluid grooves. The reservoir has a working fluid therein and is
coupled in fluid communication with the working cavity. A working
fluid flow path extends between the reservoir and the working
cavity and includes a first gap, which is disposed axially between
the first annular wall of the outer housing assembly and a first
side of the rotor portion, a second gap, which is disposed axially
between the second annular wall of the outer housing assembly and a
second side of the rotor portion, and a third gap, which is
disposed radially between the circumferentially extending wall of
the outer housing assembly and the outer circumferential surface of
the rotor portion. At least one of the first annular wall and the
circumferentially extending wall comprises a plurality of flow
altering structures that are configured to promote disturbances in
a laminar flow of the working fluid in an associated one or ones of
the first and third gaps in areas local to the flow altering
structures when the disk is rotated relative to the outer housing
assembly and a portion of the working fluid is in the working fluid
flow path.
[0046] In still another form, the present teachings provide a
method that includes: providing an apparatus having an outer
housing assembly, a disk and a reservoir, the outer housing
assembly having a working cavity, the disk being rotatable in the
outer housing assembly, the disk having a rotor portion that is
rotatably received in the working cavity, the working cavity being
in fluid communication with the reservoir; and inducing
disturbances in a laminar flow of a working fluid in a first area
that is adjacent a first surface of the working cavity as the
working fluid passes through the working cavity during operation of
the apparatus.
[0047] Further areas of applicability will become apparent from the
description provided herein. The description and specific examples
in this summary are intended for purposes of illustration only and
are not intended to limit the scope of the present disclosure.
DRAWINGS
[0048] The drawings described herein are for illustrative purposes
only of selected embodiments and not all possible implementations,
and are not intended to limit the scope of the present
disclosure.
[0049] FIG. 1 is a front elevation view of an exemplary viscous fan
clutch constructed in accordance with the teachings of the present
disclosure, the viscous fan clutch being illustrated in operative
association with an exemplary fan;
[0050] FIG. 2 is an exploded perspective view of the fan clutch of
FIG. 1;
[0051] FIG. 3 is a longitudinal section view of the fan clutch of
FIG. 1;
[0052] FIG. 4 is an enlarged portion of FIG. 3;
[0053] FIG. 5 is a perspective, partly sectioned view of another
fan clutch constructed in accordance with the teachings of the
present disclosure;
[0054] FIG. 6 is an exploded perspective view of a portion of the
fan clutch of FIG. 1, illustrating portions of an outer housing
assembly in more detail;
[0055] FIG. 7 is a rear elevation view of a portion of the fan
clutch assembly, illustrating a portion of the outer housing
assembly in more detail;
[0056] FIG. 8 is an enlarged portion of FIG. 7;
[0057] FIG. 9 is a view similar to that of FIG. 7 but illustrating
an alternatively configured portion of the outer housing
assembly;
[0058] FIGS. 10 and 11 are views similar to that of FIG. 8 but
illustrating alternatively configured portions of the outer housing
assembly;
[0059] FIG. 12 is a perspective view illustrating a portion of
another outer housing assembly constructed in accordance with the
teachings of the present disclosure;
[0060] FIG. 13 is a perspective view illustrating a portion of
another outer housing assembly constructed in accordance with the
teachings of the present disclosure;
[0061] FIG. 14 is a rear elevation view of a portion of the outer
housing assembly of FIG. 13;
[0062] FIG. 15 is a section view taken through a portion of the
outer housing assembly of FIG. 13;
[0063] FIG. 16 is a rear elevation view of a portion of another
outer housing assembly constructed in accordance with the teachings
of the present disclosure;
[0064] FIG. 17 is a perspective view of a portion of another outer
housing assembly constructed in accordance with the teachings of
the present disclosure;
[0065] FIG. 18 is an enlarged view of a portion of the outer
housing assembly of FIG. 17;
[0066] FIG. 19 is a portion of a longitudinal section view of a
viscous fan clutch that employs the outer housing assembly of FIG.
17;
[0067] FIG. 20 is a schematic illustration of a portion of a prior
art viscous fan clutch depicting a working fluid in a gap between a
disk and an outer housing assembly, the working fluid forming a
relatively thick boundary layer adjacent the prior art outer
housing assembly;
[0068] FIG. 21 is a schematic illustration of a portion of the
viscous fan clutch of FIG. 19 depicting a working fluid in a gap
between a disk and the outer housing assembly, the working fluid
forming a relatively thin boundary layer adjacent the outer housing
assembly; and
[0069] FIG. 22 is a plot that depicts isothermal combinations of
input and output speed for a prior art viscous fan clutch and the
viscous fan clutch of FIG. 19 to a predetermined maximum
temperature in which the temperature of a working fluid in these
clutches is limited to a predetermined temperature.
[0070] Corresponding reference numerals indicate corresponding
parts throughout the several views of the drawings.
DETAILED DESCRIPTION
[0071] With reference to FIG. 1, an exemplary apparatus configured
to employ shear forces to transmit rotary energy and constructed in
accordance with the teachings of the present disclosure is
generally indicated by reference numeral 10. In the particular
example provided, the apparatus is a viscous fan clutch that is
shown in operative association with a fan 12, but it will be
appreciated that the teachings of the present disclosure have
application to other devices, including without limitation
clutches, heaters and pumps.
[0072] With reference to FIGS. 2 and 3, the apparatus 10 can
comprise an input shaft 20, a disk 22, an outer housing assembly
24, and a reservoir 26. The input shaft 20 can serve as the input
member of the apparatus 10 and can be directly driven by a source
of rotary power (e.g., the input shaft 20 can be directly coupled
to or unitarily formed with an output shaft of an electric motor)
or can be coupled to a source of rotary power through an endless
power transmission means. The endless power transmission means
could comprise a belt (not shown), such as a V-belt or poly V-belt,
that could be part of a conventional front engine accessory drive
system (FEAD). The belt of the FEAD can be mounted on a plurality
of pulleys (not shown), including a crankshaft pulley, which can be
coupled to an engine crankshaft for rotation therewith, and an
accessory pulley that can be mounted to the input shaft 20 for
common rotation. Alternatively, the endless power transmission
means could comprise a chain and sprockets, or could comprise a
plurality of meshing gears.
[0073] With reference to FIGS. 3 and 4, the disk 22 can be mounted
to the input shaft 20 for rotation therewith. The disk 22 can
comprise a rotor portion 30 that can have a first side 32, a second
side 34 and an outer circumferential surface 36. The first side 32
can have a plurality of first concentric ribs 42 that are disposed
concentrically about a rotational axis A of the input shaft 20. In
the example provided, each of the first concentric ribs 42 extends
from an axial side of a body 44 of the rotor portion 30 in a
direction that is parallel to the rotational axis A and each of the
first concentric ribs 42 terminates a first rib end face 46 that is
perpendicular to the rotational axis A. Optionally, the second side
34 can have a plurality of second concentric ribs 54 that can be
disposed concentrically about the rotational axis A. In the example
provided, each of the second concentric ribs 54 extends from an
opposite axial side of the body 44 of the rotor portion 30 in a
direction that is parallel to the rotational axis A and each of the
second concentric ribs 54 terminates a second rib end face 56 that
is perpendicular to the rotational axis A. It will be appreciated
that the configuration of the first concentric ribs 42 and/or the
configuration of the second concentric ribs 54 (if included) could
deviate from the particular configurations that are depicted
herein.
[0074] The outer housing assembly 24 is the output member of the
apparatus 10 in the example provided and is supported by one or
more bearings 58 that are mounted on the input shaft 20 so as to be
rotatable about the rotational axis A independently of the disk 22
and input shaft 20. The outer housing assembly 24 can define a
working cavity 60 that can be bounded by a first annular wall 62, a
second annular wall 64 and a circumferentially extending wall 66
that is disposed between and connects the first and second annular
walls 62 and 64. In the example illustrated, the outer housing
assembly 24 comprises a first housing member 70 and a second
housing member 72 that cooperate to form the working cavity 60. The
first annular wall 62 can define a plurality of first concentric
fluid grooves 74 that can be disposed concentrically about the
rotational axis A. In the example provided, each of the first
concentric fluid grooves 74 extends into the first housing member
70 in a direction that is parallel to the rotational axis A, each
of the first concentric fluid grooves 74 terminates a first root
surface 76 that is perpendicular to the rotational axis A, and each
of the first root surfaces 76 are disposed in a common plane. If
the disk 22 includes the second concentric ribs 54, the second
annular wall 64 can define a plurality of second concentric fluid
grooves 86 that can be disposed concentrically about the rotational
axis A. In the example provided, each of the second concentric
fluid grooves 86 extends into the second housing member 72 in a
direction that is parallel to the rotational axis A, each of the
second concentric fluid grooves 86 terminates at a second root
surface 88 that is perpendicular to the rotational axis A, and each
of the second root surfaces 88 are disposed in a common plane. It
will be appreciated that the configuration of the first concentric
fluid grooves 74 and/or the configuration of the second concentric
fluid grooves 86 (if included) could deviate from the particular
configurations that are depicted herein.
[0075] The disk 22 can be received in the outer housing assembly 24
such that the rotor portion 30 is disposed in the working cavity
60. Each of the first concentric ribs 42 can be received in an
associated one of the first concentric fluid grooves 74 and if the
rotor portion 30 includes the second concentric ribs 54, each of
the second concentric ribs 54 can be received in an associated one
of the second concentric fluid grooves 86.
[0076] The reservoir 26 can be coupled in fluid communication with
the working cavity 60 and can hold a suitable working fluid, such
as a silicone fluid, therein. More specifically, a working fluid
flow path can extend between the reservoir 26 and the working
cavity 60 and can include a first gap 90, which is disposed axially
between the first annular wall 62 and the first side 32 of the
rotor portion 30, a second gap 92, which is disposed axially
between the second annular wall 64 and the second side 34 of the
rotor portion 30, and a third gap 94 that is disposed radially
between a radially inner surface 98 of the circumferentially
extending wall 66 and the outer circumferential surface 36 of the
disk 22. The first, second and third gaps 90, 92 and 94 are
typically very small (relative to the diameter of the disk 22),
typically being less than 3 mm wide (i.e., the space between the
disk 22 and the outer housing assembly 24 in any one of the first,
second and third gaps 90, 92, and 94 is typically less than 3 mm in
dimension).
[0077] The reservoir 26 can be disposed in any desired location and
need not be located within the outer housing assembly 24. In the
example provided, the reservoir 26 is defined partly by the disk 22
and partly by the first housing member 70 of the outer housing
assembly 24. If desired, a valve 100 can be employed to control
fluid communication between the reservoir 26 and the working cavity
60. In the example provided, the valve 100 is coupled to the disk
22 for rotation therewith. The valve 100 can be operated in any
desired manner, such as with a bimetallic element, an
electromagnet, or a pneumatic cylinder, for example. Fluid exiting
the working cavity 60 can be returned to the reservoir 26 via a
return line 102. The return line 102 can be formed in the outer
housing assembly 24, for example in the first housing member 70 as
shown in FIG. 3. Alternatively, the return line 102' can be formed
radially through the disk 22' as is shown in FIG. 5.
[0078] With reference to FIGS. 3, 4 and 6, the outer housing
assembly 24 can comprise a plurality of flow altering structures
110 that are configured to locally reduce a thickness of a boundary
layer of the working fluid adjacent the outer housing assembly 24
when the disk 22 is rotated relative to the outer housing assembly
24 and a portion of the working fluid is in the working fluid flow
path. In the example provided, the flow altering structures 110 are
disposed on the circumferentially extending wall 66, but it will be
appreciated that the flow altering structures 110 could be disposed
on the first annular wall 62 and/or the second annular wall 64 in
addition to or in lieu of the circumferentially extending wall 66.
Also in the example provided, the flow altering structures 110
number at least five (5) in quantity that are disposed on the
circumferentially extending wall 66.
[0079] With reference to FIG. 9, the flow altering structures 110'
can be formed as projections that extend from an interior surface
98' of the outer housing assembly 24'. In the example of FIGS. 6
through 8, however, the flow altering structures 110 comprise
cavities 120 that are formed in a radially inner surface 98 of the
circumferentially extending wall 66. Each of the cavities 120
extends radially outwardly of the radially inner surface 98 of the
circumferentially extending wall 66.
[0080] The configuration of the cavities 120 can be varied to suit
several objectives, such the ease and manner with which the
cavities 120 can be formed, the manner in which the working fluid
is drawn into the cavities 120, and/or the manner in which the
working fluid exits from the cavities 120. For example and with
reference to FIG. 10, each cavity 120 can optionally have a
radially outward wall 130 that is at least partially concentric
with the radially inner surface 98 of the circumferentially
extending wall 66. Each of the cavities 120 can have a pair of end
segments 132 that are disposed on opposite sides of the radially
outward wall 130. One or both of the end segments 132 can
optionally taper, in whole or in part, between the radially outward
wall 130 and the radially inner surface 98 of the circumferentially
extending wall 66. As another example and with reference to FIG.
11, each of the end segments 132 can connect the radially outward
wall 130 to the radially inner surface 98 of the circumferentially
extending wall 66 and optionally one or both of the end segments
132 can be defined at least partly by a radius.
[0081] Returning to FIGS. 6 through 8, the depth D of the cavities
120 can be set to any desired depth. However, we have found it to
be most practical if the cavities 120 have a radial depth D
relative to the radially inner surface 98 of the circumferentially
extending wall 66 that is greater than or equal to 0.2 mm and less
than or equal to 3.5 mm. Preferably, the radial depth of the
cavities 120 can be greater than or equal to 0.5 mm and less than
or equal to 2.8 mm. More preferably, the radial depth of the
cavities 120 can be greater than or equal to 0.8 mm and less than
or equal to 2.5 mm.
[0082] In the particular example provided, the radially inner
surface 98 of the circumferentially extending wall 66 can define a
theoretical (right circular) cylinder about which the flow altering
structures 110 are populated. The flow altering structures 110 can
be populated about the surface of the theoretical cylinder in one
or more contiguous zones and with one or more desired population
densities. For purposes of this discussion: a) the width of any
contiguous zone is defined by parallel planes that extend
perpendicular to the rotational axis A, wherein each plane is
tangent to at least one point on at least one of the flow altering
structures 110 and all of the flow altering structures 110 within
that contiguous zone are disposed axially between the two parallel
planes; and b) any contiguous zone that extends over an area that
is less than the entirety of the surface of the theoretical
cylinder has (straight) ends that are formed by intersecting planes
that include the rotational axis A and extend through the surface
of the theoretical cylinder, which is coincident with the radially
inner surface 98 of the circumferentially extending wall 66,
wherein each of the intersecting planes is tangent to at least one
point on at least one of the flow altering structures 110 and all
of the flow altering structures 110 within that contiguous zone are
disposed axially between the two intersecting planes.
[0083] For example, the flow altering structures 110 could be
disposed in a single zone that extends the entire circumference of
the theoretical cylinder (i.e., the flow altering structures 110
can be distributed over the entirety of the radially inner surface
98 of the circumferentially extending wall 66). Alternatively, the
flow altering structures 110 could be populated about the surface
of the theoretical cylinder in one or more contiguous zones and
with one or more desired population densities such that one or more
zones of the surface of the theoretical cylinder are not populated
with any of the flow altering structures 110. In the example of
FIG. 7, a zone of the surface of the theoretical cylinder is not
populated with any of the flow altering structures 110 to ensure
that the flow altering structures 110 do not interfere with the
transmission of the working fluid into the return line 102 (FIG.
6). In this example, the flow altering structures 110 are disposed
in a single contiguous zone over a sector of the circumferentially
extending wall 66, and none of the flow altering structures 110 are
disposed in a remaining sector of the circumferentially extending
wall 66 that spans at least 70 degrees. In the particular example
provided, the remaining sector of the circumferentially extending
wall 66 that is unpopulated spans about 90 degrees. Configuration
in this manner may be necessary or desirable in some situations,
for example to guard against the formation of undesirable flow
characteristics in the proximity of the return line 102 (FIG. 6) in
a configuration of the apparatus 10 (FIG. 1) that employs a wiper
element W (FIG. 12) to direct working fluid into the end of the
return line 102 (FIG. 6) that intersects the working cavity 60
(FIG. 4).
[0084] It will be appreciated, however, that the flow altering
structures 110 could be disposed in a single contiguous zone over a
sector that spans completely or nearly completely about the
perimeter of the circumferentially extending wall 66, as is shown
in FIG. 12. Moreover, a configuration of the apparatus 10 (FIG. 1)
that does not employ a wiper element, such as the embodiment of
FIG. 5, which employs a return line 102' that extends radially
through the disk 22', may benefit from a configuration in which the
flow altering structures 110 are disposed in a single contiguous
zone that spans the entire circumference of the radially inner
surface 98 of the circumferentially extending wall.
[0085] Returning to FIG. 7, because a sector of the
circumferentially extending wall 66 is not populated with the flow
altering structures 110, the flow altering structures 110 can be
thought of as being spaced in an uneven manner about the
circumference of the circumferentially extending wall 66.
Alternatively, a variable or varied spacing between the flow
altering structures 110 that are disposed within a contiguous zone
could be employed to provide uneven spacing of the flow altering
structures 110.
[0086] Within a contiguous zone that is populated by the flow
altering structures 110, the flow altering structures 110 can be
sized and populated on the radially inner surface 98 of the
circumferentially extending wall 66 such that the flow altering
structures 110 in the contiguous zone are disposed on at least 50%
of the surface area of the surface of the theoretical cylinder that
lies within the contiguous zone. More preferably, the flow altering
structures 110 in a contiguous zone can be disposed on at least 75%
of the surface area of the theoretical cylinder that lies within
the contiguous zone.
[0087] With renewed reference to FIGS. 7 and 8, when the flow
altering structures 110 are cavities 120 that are formed in the
radially inner surface 98 of the circumferentially extending wall
66, each of the cavities 120 can have an aspect ratio (AR) that is
defined by the following equation:
AR=C/R
where C is a maximum circumferential length of the cavity 120
measured at the radially inner surface 98 of the circumferentially
extending wall 66; and R is a radial distance between a radially
outer-most surface of the cavity 120 and the outer circumferential
surface 36 (FIG. 4) of the rotor portion 30 (FIG. 4) taken along a
line that intersects a rotational axis A of the disk 22 (FIG. 3).
In some forms, the aspect ratio (AR) can be greater than or equal
to 0.2 and less than or equal to 4.0. Preferably, the aspect ratio
is greater than or equal to 0.25 and less than or equal to 2.75.
More preferably, the aspect ratio is greater than or equal to 0.5
and less than or equal to 2.5. Still more preferably, the aspect
ratio is greater than or equal to 1.0 and less than or equal to
1.5.
[0088] In the example of FIGS. 13 through 15, the flow altering
structures 110a are disposed on the first annular wall 62a. The
flow altering structures 110a could comprise projections that
extend axially from the first annular wall 62a, but in the
particular example provided, the flow altering structures 110a
comprise annular wall cavities 120a that are formed in the outer
housing assembly 24a and which intersect at least one of the first
root surfaces 76.
[0089] Each of the annular wall cavities 120a can have a depth
relative to an associated one of the first root surfaces 76 that is
greater than or equal to 0.2 mm and less than or equal to 3.5 mm.
Preferably, the depth of the annular wall cavities 120a is greater
than or equal to 0.5 mm and less than or equal to 2.8 mm. More
preferably, the depth of the annular wall cavities 120a is greater
than or equal to 0.8 mm and less than or equal to 2.5 mm.
[0090] Each of the annular wall cavities 120a can have a cavity
sidewall 140 and a cavity bottom wall 142 that can be bounded by
the cavity sidewall 140. If desired, at least a portion of the
cavity sidewall 140 can be perpendicular to an associated one of
the first root surfaces 76 at a location where the portion of the
cavity sidewall 140 intersects the associated one of the first root
surfaces 76. The annular wall cavities 120a can be configured such
that at least a portion of the cavity bottom wall 142 is parallel
to at least one of the first root surfaces 76. Each of the annular
wall cavities 120a can further have a pair of opposite
circumferential ends 144. At least one of the circumferential ends
144 can be at least partly defined by a radius at a location where
the circumferential end 144 intersects an associated one of the
first root surfaces 76.
[0091] Each of the annular wall cavities 120a has an aspect ratio
(AR) that is defined by the equation:
AR=C/R
where: C is a maximum circumferential length of the annular wall
cavity 120a measured at an associated one of the first root
surfaces 76; and R is a maximum distance between the bottom wall
142 and a first rib end face 46 (FIG. 4) of an associated one of
the first concentric ribs 42 (FIG. 4) taken parallel to the
rotational axis A (FIG. 3) about which the disk 22 (FIG. 3) rotates
relative to the outer housing assembly 24a. In some examples, the
aspect ratio (AR) can be greater than or equal to 0.2 and less than
or equal to 4.0. Preferably, the aspect ratio is greater than or
equal to 0.25 and less than or equal to 2.75. More preferably, the
aspect ratio is greater than or equal to 0.5 and less than or equal
to 2.5. Still more preferably, the aspect ratio is greater than or
equal to 1.0 and less than or equal to 1.5.
[0092] The flow altering structures 110a on the first annular wall
62a can be disposed within one or more zones, with each of the
zones being coincident with an associated one of the first root
surfaces 76 and having a planar annular shape or an annular segment
shape. The flow altering structures 110a within each zone can be
sized and populated in the one or more zones such that the flow
altering structures 110a in the one or more zones can be disposed
over at least 50% of the surface area of the one or more zones.
Preferably, the flow altering structures 110a are sized and
populated within the one or more zones such that the flow altering
structures 110a in the one or more zones are disposed on at least
75% of the surface area of the one or more zones. For purposes of
this discussion, if a zone on the first annular wall 62a does not
extend completely around the first annular wall 62a, the zone can
be bounded by a pair of planes that intersect one another, each of
the planes can be tangent to one or more of the flow altering
structures 110a at one or more points, and all of the flow altering
structures 110a within that zone are disposed between the pair of
intersecting planes.
[0093] The flow altering structures 110a can be disposed on the
first annular wall 62a in any desired manner. For example, at least
a portion of the flow altering structures 110a can be disposed
about the first annular wall 62a such that they are not evenly
spaced about the circumference of the first annular wall 62a. In
this regard, a varied or variable spacing between the flow altering
structures 110a can be employed, and/or the zone or zones of the
flow altering structures 110a can be configured such that they do
not extend fully about the circumference of the first annular wall
62a. In the particular example provided, the flow altering
structures 110a are disposed in a single contiguous zone over a
sector of the first annular wall 62a, and wherein none of the flow
altering structures 110 are disposed in a remaining sector of the
first annular wall 62a that spans at least 70 degrees. In the
particular example provided, the remaining sector of the first
annular wall 62a that is unpopulated spans about 90 degrees.
[0094] In the field of viscous fan clutches, it is relatively
common for a radially outer-most one 74a of the first concentric
fluid grooves 74 to be somewhat wider than the first concentric
fluid grooves 74 that are radially inward of the radially
outer-most one 74a of the first concentric fluid grooves 74.
Consequently, it may be easier to manufacture the outer housing
assembly 24a if the flow altering structures 110a in the first
annular wall 62a were to be disposed only within the radially
outer-most one 74a of the first concentric fluid grooves 74. It
will be appreciated, however, that the teachings of the present
disclosure also extend to the use of flow altering structures 110a
in situations where they are confined solely to one or more of the
first concentric fluid grooves 74 that are radially inward of the
radially outer-most one 74a of the first concentric fluid grooves
74, as well as to situations where they are disposed on the
radially outer-most one 74a of the first concentric fluid grooves
74 and one or more of the first concentric fluid grooves 74 that
are radially inward thereof.
[0095] Those of skill in the art will appreciate that flow altering
structures 110a could be disposed on the second annular wall 64
(FIG. 3) in a manner that is similar to that described above for
the first annular wall 62a and that the use of flow altering
structures 110a on the second annular wall 64 could be in addition
to or in lieu of the flow altering structures 110a that are
disposed on the first annular wall 62a.
[0096] While the flow altering structures 110a have been described
as being circumferentially extending cavities 120a that are
disposed in or on the first concentric fluid grooves 74, those of
skill in the art will appreciate that the flow altering structures
110a could be formed somewhat differently. For example, the flow
altering structures 110a' could be formed on the first annular
surface 62a' so as to extend in a radial direction as shown in FIG.
16. In this example, the flow altering structures 110a' are
cavities 120a' that intersect a plurality of the first concentric
fluid grooves 74.
[0097] With reference to FIGS. 17 and 18, a portion of another
outer housing assembly 24b constructed in accordance with the
teachings of the present disclosure is shown. The outer housing
assembly 24b can be similar to any of the outer housing assemblies
described above, except that the flow altering structures 110b are
formed on both the circumferentially extending wall 66b and the
radially outer-most one 74a of the first concentric fluid grooves
74 in the first annular wall 62b. In this example, each of the flow
altering structures 110b comprises a first portion, which consists
of a cavity 120b-1 formed in the radially inner surface 98 of the
circumferentially extending wall 66b, and a second portion that
consists of an annular wall cavity 120b-2 that is formed in the
first root surface 76 of the radially outer-most one 74a of the
first concentric fluid grooves 74 in the first annular wall 62b.
The flow altering structures 110b in the particular example
provided were formed via an end mill (not shown), but those of
skill in the art will appreciate that the flow altering structures
110b could be formed in any appropriate manner, including casting
(e.g., die casting, investment casting, sand casting). It will be
appreciated that the sizing, population density, etc. of the flow
altering structures 110b can be similar or identical to those
described above for the first two embodiments.
[0098] With reference to FIG. 19, an apparatus 10b having an outer
housing assembly 24b constructed in the manner of FIG. 17 is
illustrated in operation wherein rotary power is provided to the
input shaft 20 to drive the disk 22 and the valve 100 is operated
in an open condition that permits fluid communication from the
reservoir 26 through the working fluid flow path to the working
cavity 60. During operation, fluid traveling through the working
fluid flow path migrates between the first and second gaps 90 and
92 and rotation of the disk 22 relative to the outer housing
assembly 24b creates a shear force in the working fluid in the
first and second gaps 90 and 92. This shear force generates a
torque that is applied against the outer housing assembly 24b and
causes the outer housing assembly 24b to rotate about the
rotational axis A. The shear forces also generate heat in the
working fluid. The working fluid in the first and second gaps 90
and 92 progressively works its way in a radially outward direction
until it is received in the third gap 94. The working fluid in the
third gap 94 is eventually directed to an inlet of the return line
102, and is returned to the reservoir 26. Due to the relatively
high viscosity of the working fluid and the relatively small size
of the first, second and third gaps 90, 92 and 94, a Reynolds
number of the working fluid in the portion of the working fluid
flow path that extends through the working cavity 60 is less than
100, which is significantly below a transition from laminar to
turbulent flow, which we understand as taking place at a Reynolds
number of about 2000. For reference, we further understand that
full turbulent flow would occur at a Reynolds number of about
4000.
[0099] With reference to FIG. 20, a greatly enlarged portion of the
working fluid in the working fluid flow path of a conventionally
configured (i.e., prior art) viscous fan clutch PAVFC is shown
(created with the aid of CFD software). For purposes of this
discussion, the prior art viscous fan clutch PAVFC is identical to
the apparatus 10b of FIG. 19, except that the prior art viscous fan
clutch PAVFC does not employ or include any of the flow altering
structures described above. As is shown, a relatively thick and
insulating boundary layer BL-1 of the working fluid between the
radially inner surface RIS of the circumferentially extending wall
CEW of the prior art outer housing assembly OHA and outer
circumferential surface OCS of the prior art rotor portion RP
stacks up against the radially inner surface RIS of the prior art
outer housing assembly OHA. The relatively thick dimension of the
boundary layer BL-1 limits heat transfer between the working fluid
and the radially inner surface RIS of the prior art outer housing
assembly OHA. In this example, the working fluid adjacent the outer
circumferential surface OCS of the prior art rotor portion RP has a
temperature of 251.degree. C., the working fluid at the indicated
point proximate the beginning of the boundary layer BL-1 has a
temperature of 219.degree. C., and the working fluid adjacent the
radially inner surface RIS of the prior art outer housing assembly
OHA has a temperature of 104.degree. C.
[0100] With reference to FIG. 21, a greatly enlarged portion of the
working fluid in the working fluid flow path of the apparatus 10b
of FIG. 19 is shown under input and output conditions that are
identical to those employed to generate the data employed in FIG.
20. As is readily apparent, the boundary layer BL-2 of the working
fluid that is adjacent the radially inner surface 98 of the
circumferentially extending wall 66b in areas local to the flow
altering structures 110b is significantly smaller in thickness,
which greatly improves the rate with which heat can be rejected
from the working fluid to the rotating outer housing assembly 24b.
In this example, the working fluid adjacent the outer
circumferential surface 36 of the rotor portion 30 has a
temperature of 164.degree. C., the working fluid at the indicated
point proximate the beginning of the boundary layer BL-2 has a
temperature of 151.degree. C., and the working fluid adjacent the
radially inner surface 98 of the outer housing assembly 24b has a
temperature of 107.degree. C. As compared to the prior art viscous
fan clutch PAVFC of FIG. 20, the temperature differential of the
working fluid that spans between the outer circumferential surface
36 of the rotor portion 30 and the radially inner face 98 of the
circumferentially extending wall 66b (in areas local to the flow
altering structures 110b) is 44.degree. C., a reduction of
71.degree. C. from the differential (i.e., 115.degree. C.) that was
obtained by the prior art viscous fan clutch PAVFC (FIG. 20).
Moreover, because of the increased rate of heat rejection (from the
working fluid to the outer housing assembly 24b), the maximum
temperature of the working fluid was reduced by 87.degree. C. in
the apparatus 10b as compared to the prior art viscous fan clutch
PAVFC (FIG. 20).
[0101] Plots in FIG. 22 depict isothermal combinations of input and
output speed for a pair of viscous fan clutches (i.e., a first or
prior art viscous fan clutch and a second viscous fan clutch that
was constructed in accordance with the teachings of the present
disclosure and which had flow altering structures) that limit the
temperature of a working fluid in these clutches to a predetermined
maximum temperature. In the particular example provided, the
predetermined maximum temperature is 232.degree. C. and as such,
each of the plots (200, 202) represents an operational speed
boundary (expressed in terms of slip heat horsepower) for a
respective one of the clutches beyond which a silicone working
fluid will rapidly degrade, causing failure of the clutch. The two
plots consist of a baseline plot 202, which depicts maximum slip
heat horsepower that the prior art viscous fan clutch of FIG. 20
can withstand prior to the working fluid therein reaching the
maximum critical temperature (i.e., the operational boundary of the
prior art viscous fan clutch) and another plot 200 that depicts
maximum slip heat horsepower that the viscous fan clutch of FIG. 19
can withstand before the working fluid reaches the maximum critical
temperature (i.e., the operational boundary of the viscous fan
clutch of FIG. 19). Each of the plots depicts maximum slip heat
horsepower of a respective one of the viscous fan clutches as a
function of the input speed of the viscous fan clutch and the fan
or output speed of the fan clutch. The data was generated per test
CS-47438.0 with a fan manufactured by BorgWarner Inc. under part
number 010023275 (O25 inch.times.9.times.2.52 inch) and a 026 inch
(660.4 mm diameter) ring shroud in conjunction with a prior art
model 664 viscous fan clutch produced by BorgWarner under part
number 010026784, which was employed to generate the baseline plot
202, or in conjunction with a model 664 viscous fan clutch produced
by BorgWarner under part number 010026784 and modified as described
in the example of FIG. 19. A line (i.e., the 50% line 210) depicts
a situation in which the fan or output speed of the viscous fan
clutch is one-half (i.e., 50%) of that of the input speed of the
viscous fan clutch. As is apparent from the two plots 202 and 200,
the maximum slip heat horsepower of the prior art viscous fan
clutch PAVFC (FIG. 20) is 3.4 HP where the baseline plot 202
intersects the 50% line 210, whereas the maximum slip heat
horsepower of the viscous fan clutch 10b (FIG. 19) constructed in
accordance with the teachings of the present disclosure is 4.0 HP
where the plot 200 intersects the 50% line 210. The 0.6 HP increase
in maximum slip heat horsepower is a 17% improvement that is a
directly attributable to the improved heat rejection capabilities
that are provided by the teachings of the present disclosure.
[0102] In view of the above discussion, a method is provided that
includes: providing an apparatus having an outer housing assembly,
a disk and a reservoir, the outer housing assembly having a working
cavity, the disk being rotatable in the outer housing assembly, the
disk having a rotor portion that is rotatably received in the
working cavity, the working cavity being in fluid communication
with the reservoir; rotating the rotor within the outer housing
assembly to generate a flow of a working fluid through the working
cavity and to apply a shear force to the working fluid flowing
through working cavity; and at a plurality of discrete locations on
the outer housing assembly where the flow of the working fluid
passes through the working cavity, inducing movement of the working
fluid in a direction that is transverse to a boundary layer of the
working fluid that is adjacent to the first annular surface. The
locations on the outer housing assembly can be where the flow of
the working fluid through the working cavity has a Reynolds number
that is less than 100.
[0103] The first surface can be formed on an annular wall of the
outer housing assembly. Additionally or alternatively, the first
surface can be formed on a circumferentially extending wall of the
outer housing assembly. As such, the method can further include
inducing disturbances in a laminar flow of the working fluid in a
second area that is adjacent to a second surface of the working
cavity as the working fluid passes through the working cavity
during operation of the apparatus.
[0104] The method can further include forming a plurality of flow
altering structures on the outer housing assembly. The flow
altering structures can be unitarily formed with a portion of the
outer housing assembly that defines a plurality of concentric fluid
grooves, and the flow altering structures can optionally be formed
as cavities. If the flow altering structures are formed as
cavities, the method can further include casting at least a portion
of the outer housing assembly, wherein at least a portion of the
cavities are formed on the portion of the outer housing assembly
when the portion of the outer housing assembly is cast.
Additionally or alternatively, the method could further include
removing material from a portion of the outer housing assembly to
form at least a portion of the cavities. Material can be removed
from the portion of the outer housing assembly in an operation
selected from a group consisting of: milling, drilling, etching,
broaching, and electro-discharge machining.
[0105] Additionally or alternatively, the method could further
include forming a portion of the outer housing assembly in an
operation selected from a group consisting of: stamping, embossing,
forging, fine blanking and knurling to form one or more flow
altering structures.
[0106] The foregoing description of the embodiments has been
provided for purposes of illustration and description. It is not
intended to be exhaustive or to limit the disclosure. Individual
elements or features of a particular embodiment are generally not
limited to that particular embodiment, but, where applicable, are
interchangeable and can be used in a selected embodiment, even if
not specifically shown or described. The same may also be varied in
many ways. Such variations are not to be regarded as a departure
from the disclosure, and all such modifications are intended to be
included within the scope of the disclosure.
* * * * *